Implantable cardiac devices are commonly used for treating patients with heart arrhythmias. These devices include well-known pacemakers and implantable cardioverter defibrillators (ICD's). In general, these devices include a lead that is adapted to be implanted in the body of the patient so as to be positioned adjacent the heart and a control unit that is also adapted to be implanted within the patient which is connected to the lead so as to deliver electrical impulses to the heart via the lead. Pacemaker devices can be very sophisticated and include sensors and processing capabilities so that pacing is provided only when needed.
In pacing applications, the lead is typically implanted within the chambers of the heart so as to be positioned adjacent the walls of the right atrium or the right ventricle. In many typical pacemakers, the leads are implanted so that the lead is positioned within the right atrium and the right ventricle chambers so that a pacing pulse can be delivered directly to cardiac cells of these chambers to induce a paced response of the heart.
There are several different types of leads that are currently in common use in pacing applications. One very common lead is a bipolar lead which includes a pacing cathode electrode and an anode electrode. The same two electrodes also serve to sense cardiac signals. The pacing pulse is delivered to the cardiac cells by the cathode and anode electrodes. Typically, the sensing by the same two electrodes is configured so as to monitor intrinsic heart activity and provide a signal indicative thereof to the control unit. Other types of leads include unipolar leads which have a single (cathode) electrode for delivering stimulation pulses to the heart and an indifferent (anode) electrode, such as the casing of the control unit which serves as the return electrode for the stimulation pulses.
As discussed above, pacemaker electrodes are typically implanted within the right atrium and right ventricle. The right atrium and the right ventricle generally provide blood circulation to the pulmonary system, i.e., circulation to the heart itself. The left atrium and the left ventricle provide circulation to the rest of the body's circulatory system including the major organs of the body such as the brain. Typically, implantation within the right atrium and the right ventricle has been preferred to implanting leads within the left atrium and the left ventricle, which has generally been thought to be too invasive of a procedure and to pose undesirable risks of complications to the flow of blood in the circulatory system. However, as the blood in the circulatory system is so primarily pumped by the left atrium and the left ventricle, pacing the right atrium and the right ventricle may not always provide optimum results in ensuring adequate cardiac activation and hemodynamics.
Consequently, there has been a desire to develop techniques for pacing the left atrium and the left ventricle. One such technique involves the implantation of transvenous leads into the coronary sinus region via the right atrium. As used herein, the phrase “coronary sinus region” refers to the coronary sinus vein, great cardiac vein, left marginal vein, left posterior ventricular vein, middle cardiac vein, and/or small cardiac vein or any other cardiac vein accessible by the coronary sinus.
The coronary sinus is a vein in the coronary circulatory system that is typically located in the heart so as to be proximal the outer walls of the left atrium and left ventricle of the heart. The coronary sinus vein opens into the right atrium through the coronary ostium (or Os), that is accessible for lead implantation. By implanting a lead within the coronary sinus region and then positioning the lead tip so that the lead's electrodes are adjacent the left atrium or the left ventricle, it is known that stimulation pulses can be provided to the left atrium or the left ventricle. This allows these chambers to be paced, resulting in improved activation without the complications associated with directly implanting leads within these chambers.
Current left heart pacing leads whose stimulation electrodes are positioned in the coronary veins, for example, are simple in design, such as a ring, partial ring, or a tip electrode. However, none of these electrode designs are designed specifically for achieving optimal electrode-tissue orientation to achieve (in turn) optimal cardiac stimulation thresholds in the coronary veins. They are not able to perform optimally as the electrodes for these leads are not able to provide electrical fields that are optimally directed towards excitable cardiac tissue.
A number of patents are typical of the prior art in this regard. U.S. Pat. No. 5,383,922 to Zipes et al. discloses an implantable lead system that includes RF electrodes for fixating the lead into position. U.S. Pat. No. 5,755,761 to Obino discloses an implantable lead system that includes partial ring electrodes for changing the delivery of the pulse. U.S. Pat. Nos. 5,999,858 and 6,144,882 to Sommer et al. and U.S. Pat. No. 6,295,475 to Morgan each discloses an implantable lead system that has a shaped tip electrode. U.S. Pat. No. 6,161,029 to Spreigl et al. discloses an implantable lead system that includes a stent-like distal electrode.
It was with knowledge of the foregoing state of the technology that the present invention has been conceived and is now reduced to practice.